In typical control valve assemblies, a valve cage may be at least partially disposed within a passageway formed in the interior of the valve body, and the valve cage may be adapted to guide a valve plug that is slidingly received into a central bore of the cylindrical valve plug. The valve cage typically has a mating protrusion disposed at or adjacent to a top portion of the valve cage, and the mating protrusion may extend around a circumference of an outer surface of the valve cage. The mating protrusion is typically formed of a planar top surface, a planar bottom surface longitudinally offset from the top surface, and a cylindrical end surface that extends from a terminal end of the top surface to a terminal end of the bottom surface. The top surface and the bottom surface are each parallel to a transverse reference plane that is normal to a longitudinal axis that is coaxially aligned with the cylindrical outer surface of the valve cage.
To couple the valve cage to the control valve assembly, a top portion of the mating protrusion is disposed within an annular bonnet recess formed at a bottom portion of the bonnet, and a bottom portion of the mating protrusion is disposed within an annular body recess formed on a top portion of the valve body. When the bonnet is coupled to the valve body by a plurality of bolts, a planar bonnet mating surface engages the top surface of the mating protrusion and a planar body mating surface engages the bottom surface of the mating protrusion. Because the bonnet mating surface and the body mating surface are parallel to the top surface and the bottom surface, respectively, of the mating protrusion, the compressive force resulting from the clamping act on the planar top surface in a direction normal to the top surface, and also acts on the planar bottom surface in a direction normal to the bottom surface. Because the clamping load acts normal to the top and bottom surfaces of the mating protrusion, the maximum allowable clamping force must be less than the maximum force that can be applied to the material without resulting in plastic deformation of the material.